| Due to the limitations of the traditional short fiber reinforced composites in the fiber length and the fiber content,and relatively high manufacturing costs and lower processing efficiency of continuous fiber reinforced composite,long fiber reinforced thermoplastic resin matrix composites have attracted more and more attention in aviation and automobile industries due to their high mechanical properties and industrial automation.The long fiber reinforced composites with polyether ether ketone(PEEK)resin as matrix are promising,Since PEEK is a kind of high performance engineering plastics with excellent comprehensive properties.However,due to its good solvent resistance and high melt viscosity,Polyether ether ketone(PEEK)is faced with the core technical problems of melt impregnation and fiber dispersion in the preparation process.Therefore,the preparation method of the long fiber reinforced composite material for the PEEK has important research significance.In this paper,PEEK fiber and carbon fiber were cut short,and then long carbon fiber reinforced PEEK composite was obtained by molding three-dimensional needled CF/PEEK preform prepared.The whole preparation and molding process is more simple compared with the past mode,the fiber content can be accurately controlled,the cost is lower,the large-scale production is easy to form,no solvent is involved in the whole process,and it is environmentally friendly.The long fiber improves the mechanical property and the continuity of the composite material,and the fiber dispersion is improved during the mixing and carding process of the two fibers,providing convenience for the later part of process.The fiber hybrid mode of three-dimensional needled structure provides multidirectional flow and impregnation channels for melt resins,which is beneficial to improve the impregnation effect of the plate,improve the mechanical properties,and reduce the ratio difference of the longitudinal and transverse strength.In this paper,the effect of the molding process on the mechanical properties of the composite is studied.The results of the orthogonal test of a L16(4~5)show that the influence of the molding temperature and the molding time on the CF/PEEK composite is the most obvious.The impact of the molding pressure is relatively small and the effect of the cooling rate is negligible in the scope of the study.The optimal level of the process parameters was 415?,30 min,4 MPa and 20?/min.The effects of fiber content on the mechanical properties,thermal properties and crystallization properties of the composites were further studied in the range of 30-60wt%.Within the scope of the study,when the content of reinforced fiber was increased from 40 wt%to 50 wt%,the mechanical properties of the composite increased little,the ratio difference between longitudinal and transverse strength of the composite was close to 1,and when the content of reinforced fiber increased from50 wt%to 60 wt%,The increase of mechanical properties is the largest,but the ratio difference between longitudinal and transverse strength of composite increases and isotropic behaviour of composites weakens.Although no significant change in the crystallization properties was seen with the increase of fiber content,The melting point and the temperature of 5%thermal weight loss of composites increased.The Heat deflection temperature increased,indicating that the thermal properties of the composites were markedly improved.The results of micro-morphology show that dispersion of fibers and the wettalility in the 30–50 wt%content range is better than that of 60 wt%content fiber.Although the fiber strengthening is dominant in the mechanical properties of the composites,The appearance of dry fiber and resin-rich zone is obvious in the composites with 60 wt%fiber content.This suggested that three-dimensional(3D)needle-punched CF/PEEK composites simultaneously achieve both mechanical properties and manufacture-ability for molding parts. |
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